How Much HP Can a 8 3/4 Handle?

I find this to be one of the most Hot/Cold discussed topics when you dive into it.
My 2700 lb dart with 620 ish HP, footbraking into the 10.40's has had the same 8.75 w. suregrip in it for probably 10 years. car pulls the wheels about 6 inches off the ground.

I called a popular drivetrain company to buy parts/build another 8.75 for my powertour car, and was pretty much talked out of a 8 3/4 for anything over 3000 lbs, and 600+ HP.
I gave the usual rebuttals...
But its an auto, but its footbrake, but its not THAT heavy...but i have one in my Dart... The guy was knowledgeable, and super friendly, but that was his firm belief.

Makes it tough :p